At present, some stepless transimission mechanisms are known, that basically consist on a pair of pulleys mounted on parallel shafts and the movement transmission between them is obtained by means of a trapezoidal cross section belt. Each one of these pulleys is constituted by two interlocked coaxial trunco-conical plates or pieces, which their internal face to face shapes are of trunco-conical configuration. The trunco-conical plates and pieces of each pulley can be shifted between them, moving away or aproaching, modifying in this manner the annular zones where the belt will be supported. When aproaching, the trunco-conical plates or pieces of each pulley, the radii of the annular zones where the belts lie will be increased. On the other way, when moving away, the trunco-conical plates or pieces of each pulley, the contrary is obtained. These radii variations in the pulleys permit to obtain a continuous variation of the transmision ratio.
Based on the stepless transmission idea, the dutch Company DAF, released to the market (possibly at the beginning of the second half of the century) its passenger car DAF-44, equipped with a stepless transmission (Variomatic) developped by his inventor Mr. Doorne and the above Company.
Recently, FIAT released its passenger car FIAT UNO SELECTA and FORD its own passenger car FORD FIESTA CTX. Both models are equipped with stepless transmission or continuous variation transmissions and both mechanisms, which are based on the trunco-conical pulleys already described above and on a special ""belt"" developed among FORD, FIAT AND VAN DOORNE TRANSMISSIE. The above "belt" is made of steel sheetings mounted on flexible straps constituted by ring links, also flexible.
At last and very recently, LANCIA Company has released to the market its model Y 10 SELECTRONIC, also equipped with a stepless transmission based on the same elements used on the above mentioned motor vehicles.
It is interesting to outline that the metallic "belt", above described, has overcome the main problem of the conventional "belt", made of rubber or elastomeric materials with or without reinforcements trends, that is the low value Of the peak power that could be transmitted. With the metallic "belt", this problem has been overcome because it works under compression conditions instead of traction conditions.
The above mentioned metallic "belts" and the trunco-conical pulleys have provided an important improvement in the amount of the maximum power to be transmitted, in a continuous form in its speed variation, allowing an special application in the automotive field, In spite of it, the amounts of maximum power that has been transmitted are relatively low, so that these stepless transmissions can only be used on motor vehicles with low power engines,